Stock-based compensation - Summary of stock option activity (Details) - USD ($)	10 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Shares
Shares outstanding, beginning balance		1,824,973
Shares granted	1,020,234	763,320	994,748
Shares exercised	(13,572)	(8,516)	(47,280)
Shares canceled or forfeited		(423,527)
Shares outstanding, ending balance		2,156,250	1,824,973
Shares exercisable		875,868
Shares vested or expected to vest		2,117,832
Weighted-Average Exercise Price
Shares outstanding, beginning balance, weighted average exercise price (in usd per share)		$ 8.34
Shares granted, weighted average exercise price (in usd per share)		10.03
Shares exercised, weighted average exercise price (in usd per share)	$ 0.60	2.59	$ 8.63
Shares canceled or forfeited, weighted average exercise price (in usd per share)		9.86
Shares outstanding, ending balance, weighted average exercise price (in usd per share)		8.66	$ 8.34
Shares exercisable, weighted average exercise price (in usd per share)		7.49
Shares vested or expected to vest, weighted average exercise price (in usd per share)		$ 8.64
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted average remaining contractual term		7 years 11 months 9 days	8 years 10 months 24 days
Exercisable, weighted average remaining contractual term		6 years 10 months 13 days
Vested or expected to vest, weighted average remaining contractual term		7 years 11 months 1 day
Outstanding, aggregate intrinsic value		$ 1,605,684	$ 9,073,673
Exercisable, aggregate intrinsic value		1,082,490
Vested or expected to vest, aggregate intrinsic value		$ 1,594,651